1. 6.5 Traits and Probability
Set up Cornell Notes on pg. 73
Topic: 6.5 Traits and Probability
Essential Questions:
How did Mendel’s dihybrid crosses help him develop his “Law of Independent Assortment”?
6.5 Traits and Probability
2.1 Atoms, Ions, and Molecules
How did Mendel’s dihybrid crosses help him develop his “Law of Independent Assortment”?
KEY CONCEPT The inheritance of traits follows the rules of probability.

2. KEY CONCEPT The inheritance of traits follows the rules of probability.

3. Punnett squares illustrate genetic crosses.
The Punnett square is a grid system for predicting all possible genotypes resulting from a cross.
The axes represent the possible gametes of each parent.
The boxes show the possible genotypes of the offspring.

4. A monohybrid cross involves one trait.
Monohybrid crosses examine the inheritance of only one specific trait.
Ex: color of flower

5. G G g G g g G g G g G g Genotype= Gg Phenotype= 100% Green
Punnett Squares
A green pea plant (GG) is crossed with a yellow pea plant (gg) G G
Genotype= Gg g G g g G
Phenotype=
100% Green g G g G g

6. A purple flowered plant (Pp) is crossed with a white flowered plant (pp). What are the genotype and phenotype of the offspring?
A long tailed cat (TT) is crossed with a short tailed cat (tt). What are the genotype and phenotype of the offspring? Is it possible to have short tailed offspring?

7. Pp pp pp Pp Tt Tt Tt Tt P T T t t p p p G: Pp, pp P: 50% purple
50% white p T T Tt Tt
G: Tt t
P: 100% long tail
NO!!!! Tt Tt t

8. A testcross is a cross between an organism with an unknown genotype and an organism with the recessive phenotype. bb
BB or Bb

9. Sponge Bob Genetics: Monohybrid Crosses (In Pairs)

10. A dihybrid cross involves two traits.
Ex: color of peas & shape of peas

11. A dihybrid cross involves two traits.
Y=Yellow Pea y= Green Pea
R= Round Pea r= Wrinkled Pea
YyRr YR Yr yR yr

12. YY, Yy=Yellow Pea yy= Green Pea
RR, Rr = Round Pea rr= Wrinkled Pea

13. Please figure out the ratio.
Can use ratio when determining phenotype
Write the # biggest to smallest
Please figure out the ratio.
9: Yellow smooth
3: Yellow wrinkled
3: Green smooth
1: Green wrinkled
9:3:3:1
Will follow Dominance patterns

14. Investigation (Pg. 72 in Notebook)
In Pairs complete the “Allele Combinations and Punnett Squares” Investigation on pg. 188 in the textbook
Read the background information
Set up your dihybrid cross
Answer the 4 questions

15. RR or Rr= purple kernels rr= yellow kernels TT or Tt= Smooth kernels
tt= wrinkled kernels
Genotype:
Ratio:

16. Rt Rt rt rt RT rT
RRTt
Genotype:
Ratio:

17. Rt Rt rt rt RT rT RRTt RrTt rrTt Genotypes: RRTt, RrTt, rrTt
Phenotypes: 12: Purple Smooth Kernels
4: Yellow Smooth Kernels
reduce= 3:1

18. Genotypes: RRTt, RrTt, rrTt Phenotypes: Purple smooth, yellow smooth
1. List the genotypes and phenotypes produced by this cross:
Genotypes: RRTt, RrTt, rrTt
Phenotypes: Purple smooth, yellow smooth
2. What is the genotypic ratio resulting from this cross? The phenotypic ratio?
Genotypic: 4RRTt: 8RrTt: 4rrTt = 1:2:1
Phenoypic: 12:4 purple-smooth to yellow-smooth = 3:1
3. If the genotypes for kernel texture of two plants are tt and tt, what is the probability of their having offspring that have smooth kernels? Why?
Zero; neither parent plant has a dominant allele (T).
4. Suppose that corn plant C has a known genotype of RRTT. Could corn plants with cobs that had some yellow and wrinkled kernels be produced by crossing Plant C with a plant with a genotype of your choice? Why or why not?
No. All alleles are dominant, therefore no cross could lead to a recessive phenotype.

19. These findings led to Mendel’s second law:
The law of independent assortment states that allele pairs separate independently of each other during meiosis.
Ex:
Hair color is inherited independently from eye color
Pea color is inherited independently from pea shape
Hair line inherited independently from earlobes

20. Probability is the likelihood that something will happen.
predicts an average number of occurrences, not an exact number of occurrences.
Probability =
number of ways a specific event can occur
number of total possible outcomes .

21. Sponge Bob Genetics: Dihybrid Cross